1. Field of the Invention
The present invention relates to a cleaning sheet for wiping an object to be cleaned; more specifically, this invention relates to a cleaning sheet suitable for use in a state impregnated with liquid such as water.
2. Description of the Related Art
Cleaning sheets designed to be mounted on a mop-like holder for wiping a floor surface or the like have generally been of two types, namely, a liquid retaining type to be used in a state impregnated with liquid (water or cleaning chemical), or a dry type to be used without retention of liquid. The liquid retaining type is suitable for wiping off fine dust attached to a floor surface or the like; the dry type is advantageously effective in removing lint, hair or the like.
Patent Publications 1 to 4 disclose cleaning sheets of the above-mentioned liquid retaining type.
Patent Publication 1 (Japanese Utility-Model Registration No. 2516320) discloses a cleaning sheet with a substrate sheet disposed on a porous polymer for retaining a liquid active material. On its paper surface, the substrate sheet has a flattened outer wiping layer which is formed by thermally fusing thermoplastic fibers or by lamination of a film with pinholes. When used for cleaning, the porous polymer discharges the liquid active material onto the surface of the outer wiping layer.
Patent Publication 2 (Japanese Unexamined Patent Publication No. H10-286206) discloses a cleaning sheet with a liquid-permeable surfacing sheet disposed on a liquid retaining absorbent sheet, wherein the surfacing sheet is formed of a fiber blend including pulp fibers and thermoplastic fibers.
Patent Publication 3 (Japanese Unexamined Patent Publication No. H11-206661) discloses a cleaning sheet composed of a fiber aggregate with irregularities for retaining liquid and a liquid-permeable outer layer sheet covering the fiber aggregate, wherein the outer layer sheet may be spunlaced nonwoven fabric containing hydrophilic fibers.
Patent Publication 4 (Japanese Patent Registration No. 3042737) discloses a cleaning sheet with a microfiber layer entirely formed of microfibers having a fineness of 0.5 denier or less and disposed on a hydrophilic fiber layer formed of cotton fibers, rayon fibers or the like. This cleaning sheet can absorb wet dirt with the hydrophilic fiber layer. Alternatively, the hydrophilic fiber layer may be impregnated with chemical so as to remove dirt with the chemical being fed to the surface of the microfiber layer.
When used in a state impregnated with water or chemical, the cleaning sheets of the conventional liquid retaining type let out the water or chemical all over the cleaning surface. Accordingly, dust attached to a floor surface or the like can be wiped off with the aid of water. However, when a freely movable, relatively large refuse such as lint, hair and the like lies on a floor surface, these cleaning sheets cannot collect the refuse sufficiently only through the adsorptivity of water.
In addition, since water fed to the contact surface of the cleaning sheet against an object to be cleaned, such as floor surface results in formation of water film between the cleaning sheet and the object to be cleaned, resistance will be extremely increased when the cleaning sheet is moved.
In Patent Publication 1, since the surface of the outer wiping layer is flattened by thermally fusing, thermoplastic fibers until they lose the fibrous shape or by lamination of a resin film, the water film between the cleaning sheet and the object to be cleaned increases resistance in wiping operation. In addition, since the cleaning surface is flat, dirt adhered to a floor or the like is difficult to remove.
In Patent Publications 2 and 3, since hydrophilic fibers such as pulp fibers and rayon fibers appear on the cleaning surface to let out absorbed water in a short period of time, these cleaning sheets are unfit for prolonged cleaning. Furthermore, the hydrophilic fibers appearing on the cleaning surface increase frictional resistance to a floor surface or the like, increasing resistance in wiping operation.
In Patent Publication 4, since the cleaning surface is formed only of microfibers having a fineness of 0.5 denier or less, the water film is liable to be formed between the cleaning surface and the object to be cleaned, increasing resistance in wiping operation. Moreover, since the cleaning surface only of such microfibers is substantially flat, the effect of wiping off dirt is deteriorated.